This invention relates to a marine propulsion system, and more particularly to an inboard-outboard type marine propulsion system.
The invention is designed to reduce or eliminate noise and vibration from an inboard mounted engine. The invention further provides an outboard mounted gearcase and drive unit, and a system for transferring power from the inboard mounted engine to the outboard mounted drive unit. The drive unit is mounted so as to be pivotable about a horizontal tilt axis, and steerable about a vertical steering axis.
In accordance with the invention, a marine propulsion system for use in a boat includes an engine adapted for mounting in the aft portion of the boat adjacent the transom. The engine is oriented so that its axis is substantially transverse to the axis of the boat. With this orientation, the engine crankshaft extends substantially parallel to the boat transom. A drive unit is mounted to the exterior of the transom, and includes a propeller interconnected with power transfer means for driving the propeller in response to rotation of the engine crankshaft. Drive means is provided for drivingly interconnecting the engine crankshaft with the power transfer means. In one embodiment, the engine is mounted in a chamber at the aft end of the boat for isolating the engine from the interior of the boat. One wall of the chamber is defined by the transom. The engine is mounted in the chamber by resilient mounting means for isolating the boat from engine vibrations. The drive unit is rigidly mounted to the exterior of the boat transom, and the power transfer means includes means for accommodating movement of the engine crankshaft resulting from engine vibration. The power transfer means includes a rotatable shaft disposed in the upper end of the drive unit defining a tilt axis about which the drive unit is pivotable. The engine crankshaft is interconnected with a rotatable output means, such as a sprocket, and the rotatable shaft in the upper end of the lower unit is provided with rotatable input means, such as a sprocket. A chain is provided about the output and input sprockets for transferring power therebetween. The means for accommodating movement of the engine crankshaft is preferrably associated with the output sprocket interconnected with the engine crankshaft. In one embodiment, the means for accommodating movement of the engine crankshaft includes a drive shaft interconnected with the engine crankshaft through a first flexible joint, such as a universal joint. The drive shaft is connected at its other end to the rotatable output sprocket through a second flexible joint, such as a universal joint. With the provision of universal joints at both ends of the drive shaft, engine vibration is isolated from the sprocket and thereby has little or no effect on the operation of the drive unit. In one embodiment, the sprocket is an axially extending hollow member, and the drive shaft extends substantially coaxially in the interior of the sprocket. The drive shaft is connected to an end of the passage in the hollow sprocket, and the teeth of the sprocket are located about the outer periphery of the sprocket at its other end.